1. Field of the Invention
The present invention relates to a direct-injection spark-ignition engine in which an end of an injector is located inside a combustion chamber such that a mist of fuel sprayed from the injector is locally distributed in the proximity of an electrode of a spark plug.
2. Description of the Related Art
There exists a conventionally known direct-injection spark-ignition engine which is provided with a spark plug and an injector for feeding fuel directly into a combustion chamber to achieve an improvement in fuel economy by stratified charge combustion. In this kind of engine, it is necessary to accelerate evaporation and atomization of the fuel while minimizing dispersion of the fuel and to maintain a condition under which an ignitable mixture of an appropriate air-fuel ratio is locally distributed around an electrode of the spark plug.
Techniques for achieving such objectives are disclosed in Japanese Unexamined Patent Publication Nos. 1998-54246 and 2001-248443, for example, in which the fuel is injected directly to the proximity of an electrode of a spark plug such that the fuel would scarcely go into contact with cylinder walls or a piston in a combustion chamber.
These prior art examples, however, have a problem that the fuel sprayed toward the electrode of the spark plug is apt to form droplets around the electrode and stick thereto. The fuel droplets adhering to the electrode and its surrounding areas could cause an electric leakage resulting in an ignition failure. Another problem of the prior art examples is that the mixture could become excessively rich around the electrode. It has conventionally been desired to solve these problems because they would cause a reduction in engine power, deterioration of fuel economy or an increase in the amount of emissions.